Bring 6 to 8 quarts of water to boil for the fettuccine.,Meanwhile, soften the onion in the butter in a skillet.,If they are gritty, rinse the morels quickly under running water.,Slice the caps and chop the stalks.,Add the morels to the onions with the stock.,Simmer for 10 to 15 minutes, stirring occasionally.,Season to taste with salt and pepper.,Cook the fettuccine until al dente.,______,Toss immediately and serve, passing the Parmesan cheese separately.